Ion-exchange membrane

ABSTRACT

A polymerizable composition for forming an ion-exchange resin precursor, the polymerizable composition containing a monomer component and polyethylene particles in an amount of 50 to 120 parts by mass per 100 parts by mass of the monomer component, wherein the monomer component contains an aromatic monomer for introducing ion-exchange groups and a nitrogen-containing aliphatic monomer, the nitrogen-containing aliphatic monomer being present in an amount of 10 to 35% by mass in said monomer component. An ion-exchange membrane is produced by applying the polymerizable composition onto a polyolefin type filament base material and polymerizing the polymerizable composition to form an ion-exchange resin precursor and, thereafter, introducing ion-exchange groups into the precursor.

TECHNICAL FIELD

This invention relates to an ion-exchange membrane. More specifically,the invention relates to a polymerizable composition for forming anion-exchange resin precursor for use in the production of anion-exchange membrane, to a method of producing an ion-exchange membraneusing the same composition, and to an ion-exchange membrane obtained bythe same method.

BACKGROUND ART

Ion-exchange membranes have a structure in which an ion-exchange resinis held in a specific base material. The membrane has only a smallstrength when it is formed by using the ion-exchange resin alone. Whenused being immersed in a liquid, further, the membrane swells andundergoes a large change in its form, and is not suited for thepractical use. Therefore, the ion-exchange membrane has been used in aform that is obtained by holding an ion-exchange resin in a basematerial that has a predetermined strength so will not to swell, so willnot to change its form, and so will not to impair the ion-exchangecapability specific to the ion-exchange resin.

It is a widely accepted practice that the above ion-exchange membraneuses a woven fabric of polyvinyl chloride as the base material. However,the ion-exchange membrane using the polyvinyl chloride as the basematerial has some defects, i.e., small resistance against the heat andsmall resistance against the chemicals. In recent years, therefore,study has been forwarded extensively concerning the ion-exchangemembranes using a polyolefin such as polyethylene or polypropylene asthe base material.

The ion-exchange membranes using the polyolefin as the base materialhave very larger resistance against the heat and chemicals than thoseusing the polyvinyl chloride as the base material, but also have pooradhesiveness between the polyolefin base material and the ion-exchangeresin. Therefore, the ion-exchange resin and the base material tend toseparate away from each other after they are subjected to the swellingand drying (shrinking) repetitively. As a result, the ion-exchangemembrane is accompanied by such problems as a decrease in the functionas the diaphragm, an increase in the permeation of water therethroughand a decrease in the current efficiency. Moreover, a decrease in theadhesiveness between the polyolefin base material and the ion-exchangeresin results in a decrease in the durability, as a matter of course.

As a means for improving the adhesiveness between the polyolefin basematerial and the ion-exchange resin, there can be, usually, considered ameans for treating the surfaces of the polyolefin base materials by theirradiation with electron rays or by the treatment with coronadischarge. Such a means, however, requires an apparatus of a large scaleand, besides, impairs the strength of the polyolefin base material, andcannot be put into practice without difficulty. Therefore, a variety ofmeans have been proposed for improving the adhesiveness.

For example, a patent document 1 proposes an ion-exchange membraneusing, as the base material, a woven fabric comprising a multifilamentof a polyethylene having a weight average molecular weight of not lessthan 10⁵ (so-called high molecular polyethylene). There is describedthat the ion-exchange membrane features not only an improved strengthdue to the multifilament of the very high molecular polyethylene butalso an improved adhesiveness between the ion-exchange resin and thebase material because of an increase in the contact area between them.

However, the very high molecular polyethylene is a special polymer thatis very difficult to form based on an ordinary method, and is veryexpensive. Besides, the woven fabric comprising the multifilamentthereof is very difficult to obtain.

Therefore, there has been urged to develop a means for improving theadhesiveness even by using a monofilament woven fabric that is availableeasily and inexpensively.

Further, a patent document 2 proposes a method of producing anion-exchange membrane by applying, onto a base material of apolyethylene fabric, a monomer paste that contains fine polyethyleneparticles of a particle size of not more than 10 μm for forming anion-exchange resin precursor, polymerizing the monomer paste and,thereafter, introducing ion-exchange groups into the thus formedion-exchange resin precursor. According to this method, the finepolyethylene particles work as a thickener and hence impart a suitabledegree of viscosity and spinnability to the monomer paste which,therefore, can be evenly adhered to the base material of polyethylenefabric. Further, the obtained ion-exchange membrane forms an island-seastructure comprising the polyethylene that is distributed like a sea andthe ion-exchange resin that is distributed like islands. Thepolyethylene continuing like the sea melt-adheres to the base materialof the polyethylene fabric. Therefore, the adhesion is improved betweenthe base material and the ion-exchange resin despite the base materialis made from the woven fabric of monofilaments.

This method, however, requires the heat treatment at a high temperatureto melt the base material of the polyethylene fabric and is, therefore,accompanied by a problem of a decrease in the mechanical strength of theion-exchange membrane that is obtained. Besides, even if an improvedadhesiveness is once obtained, gaps develop between the base materialand the ion-exchange resin as the ion-exchange resin swells andcontracts repetitively, permitting water to permeate through inincreasing amounts and, as a result, causing a decrease in the electriccurrent efficiency. Therefore, it has been urged to further improve theadhesiveness.

Moreover, a patent document 3 is proposing a method of producing anion-exchange membrane by using fine particles of anethylene/polyethylene modified with α-unsaturated carboxylic acid, suchas acrylic acid-modified polyethylene (fine particles of acid-modifiedpolyethylene), instead of using the fine polyethylene particles that areused by the method of the above patent document 2.

The above method is to improve the method of the patent document 2, andforms an island-sea structure comprising the acid-modified polyethylenedistributed like a sea and the ion-exchange resin distributed likeislands. According to this method, a high degree of adhesiveness issecured between the sea-like acid-modified polyethylene and theisland-like ion-exchange resin since affinity is high between theacid-modified fine polyethylene particles and the monomer for formingthe ion-exchange resin (or precursor) and, besides, since a graftpolymerization takes place in the interface between the acid-modifiedfine polyethylene particles and the island-like ion-exchange resin.

According to this method, however, despite the adhesiveness is securedbetween the sea-like acid-modified polyethylene and the island-likeion-exchange resin, the adhesiveness is not improved between thepolyethylene base material and the ion-exchange resin. Specifically,when the base material is a woven fabric of inexpensive monofilaments,the contact area is not secured to a sufficient degree between theion-exchange resin and the base material still leaving, therefore, theproblem of lack of adhesiveness.

PRIOR ART DOCUMENTS Patent Documents

Patent document 1: JP-A-6-322156Patent document 2: Japanese Patent Publication No. 6-37568Patent document 3: Japanese Patent No. 3461991

OUTLINE OF THE INVENTION Problems that the Invention is to Solve

It is, therefore, an object of the present invention to provide anion-exchange membrane that secures excellent adhesiveness between apolyolefin type base material and an ion-exchange resin, to provide acomposition used for the production of the ion-exchange membrane, and toprovide a method of producing the ion-exchange membrane.

Means for Solving the Problems

In producing ion-exchange membranes based on a customary method, thepresent inventors have discovered that there can be obtained anion-exchange membrane that exhibits excellent adhesiveness between thepolyolefin base material and the ion-exchange resin if anitrogen-containing aliphatic monomer as represented by acrylonitrile ismade present in a monomer that is used for producing an ion-exchangeresin precursor (resin having a functional group capable of introducingan ion-exchange group), and have thus completed the invention.

According to the present invention, therefore, there is provided apolymerizable composition for forming an ion-exchange resin precursor,the polymerizable composition containing a monomer component andpolyethylene particles in an amount of 50 to 120 parts by mass per 100parts by mass of the monomer component, wherein the monomer componentcontains an aromatic monomer for introducing ion-exchange groups and anitrogen-containing aliphatic monomer, the nitrogen-containing aliphaticmonomer being present in an amount of 10 to 35% by mass in the monomercomponent.

In the polymerizable composition for forming the ion-exchange resinprecursor, it is desired that:

(1) The nitrogen-containing aliphatic monomer is an acrylonitrile; and(2) The polyethylene particles are unmodified polyethylene particles.

According to the present invention, further, there is provided a methodof producing an ion-exchange membrane by applying the abovepolymerizable composition onto a polyolefin type filament base materialand polymerizing the composition to form an ion-exchange resin precursorand, thereafter, introducing ion-exchange groups into the precursor.

In the above method of production, it is desired that:

(1) The polyolefin type filament base material is a polyolefin typemonofilament base material; and(2) The polyolefin type filament base material is a polyethylene typefilament base material.

Further, according to the present invention, there is provided anion-exchange membrane obtained by the above-mentioned method ofproduction.

That is, the ion-exchange membrane has a structure in which an ionexchanger is filled in the voids in the polyolefin type filament basematerial, and is obtained by the above-mentioned method of production.Therefore, the ion-exchange membrane has a water permeability of notmore than 50 ml/(m²·hour) as measured by using the water under apressure of 0.1 MPa.

Moreover, the ion exchanger contains an aromatic ion-exchange resin anda polyethylene as the resin components.

The aromatic ion-exchange resin contains a constituent unit derived fromthe nitrogen-containing aliphatic monomer.

In the invention, the unmodified polyethylene stands for a polyethylenethat has not been modified with acid, i.e., stands for a polyethylenefree of constituent units that are derived from the comonomers havingacid groups such as of acrylic acid or anhydrous maleic acid.

Effects of the Invention

In the ion-exchange membrane of the present invention, the voids in thepolyolefin type filament base material are filled with the ionexchanger. The ion-exchange membrane is the same as the conventionalion-exchange membranes in regard to that it has a sea-island structurein which the ion-exchange resin is distributed like islands in thepolyethylene that is distributed like a sea being derived from thepolyethylene particles. Here, however, an important feature resides inthat the constituent units derived from the nitrogen-containingaliphatic monomer have been introduced in the ion-exchange resin.

Namely, since the constituent units have been introduced, theion-exchange resin exhibits excellent adhesiveness to the polyethylenedistributed like the sea and to the polyolefin type filament basematerial, and suppresses the water permeability to lie in a range whichis as low as not more than 50 ml/(m²·hour) as measured by using thewater under a pressure of 0.1 MPa.

Though the mechanism for exhibiting such excellent adhesiveness has notyet been known in detail, it is considered that the adhesivenessincreases since the ion-exchange resin becomes more flexible as it hasthe constituent units derived from the nitrogen-containing aliphaticmonomer. As a result, the ion-exchange resin is less likely to beseparated from the polyolefin filament base material despite theion-exchange resin is unavoidably swollen and shrunk in the process ofproducing the ion-exchange membrane. Moreover, it is estimated that theion-exchange resin and the polyolefin that constitutes the base materialhave main chain structures that are similar to each other exhibiting,therefore, improved affinity to the polyolefin filament base material.

Here, the water permeability which is low means that the gaps are formedin small amounts in the step of producing the exchange membrane or whena predetermined pressure is applied at the time of measuring the waterpermeability. Namely, this means that the ion-exchange resin has beenfirmly adhered to the polyolefin type filament base material and to thesea-like polyethylene. In the ion-exchange membrane of the presentinvention, therefore, the base material is firmly adhered to the ionexchanger that is filled in the voids in the base material. As a result,the ion-exchange membrane features excellent durability, small electricresistance and high current efficiency when it is used for theelectrodialysis or the like.

In the present invention, the above-mentioned excellent adhesiveness isrealized not only when the base material is made from the multifilamentsbut also when the base material is made from the monofilaments which areeasily available and inexpensive. This makes the greatest advantage ofthe present invention.

MODES FOR CARRYING OUT THE INVENTION

The ion-exchange membrane of the present invention is produced by usinga specific polymerizable composition for forming an ion-exchange resinprecursor, by applying the polymerizable composition onto a polyolefintype filament base material, executing the polymerization in this stateto form an ion-exchange resin precursor and, finally, introducingion-exchange groups into the precursor.

<Composition for Forming the Ion-Exchange Resin Precursor>

The ion-exchange membrane of the present invention is formed by using apolymerizable composition for forming an ion-exchange resin precursor.Namely, the polymerizable composition is polymerized to, first, form theion-exchange resin precursor. The ion-exchange resin precursor is apolymer which, by itself, has no ion-exchange group but has a functionalgroup that is capable of introducing an ion-exchange group. Therefore,the ion-exchange resin is formed by reacting the above precursor with acompound having an ion-exchange group.

In the invention, the polymerizable composition for forming theion-exchange resin precursor (hereinafter often called simplypolymerizable composition) contains a monomer component for forming theion-exchange resin precursor by polymerization and a polymerizationinitiator, and, further, contains polyethylene particles for impartingspinnability and viscosity that is necessary for evenly adhering thepolymerizable composition to the polyolefin type filament base material.

1. Monomer Component;

As the monomer component, the invention uses an aromatic monomer forintroducing an ion-exchange group to form a basic skeleton of theion-exchange resin precursor (or ion-exchange resin), a cross-linkablemonomer, and a nitrogen-containing aliphatic monomer for forming aconstituent unit that is introduced into the basic skeleton of theion-exchange resin precursor (or ion-exchange resin) and that greatlycontributes to improving the adhesiveness.

(1-1) Aromatic Monomer for Introducing an Ion-Exchange Group;

The aromatic monomer for introducing an ion-exchange group is amonofunctional compound that has a radically polymerizable group andthat, further, has a functional group for introducing an ion-exchangegroup. The monomer having such a group has also been used for producingthe conventional ion-exchange membranes. In the present invention,however, the monomer having the above group must be the aromatic one,i.e., the monomer having an aromatic group in the molecules thereof.This is because the aliphatic monomer having no aromatic group becomesso flexible that there cannot be formed an ion-exchange resin that has apredetermined strength or stability in the form.

The aromatic monomer has a radically polymerizable unsaturated group andan aromatic group, and is selected from those that are used when acation-exchange resin is to be formed (i.e., monomers having afunctional group for introducing a cation-exchange group) or from thosethat are used when an anion-exchange resin is to be formed (i.e.,monomers having a functional group for introducing an anion-exchangegroup). In either case, there can be used the monomers known per se.

As the monomer having a functional group for introducing acation-exchange group, there can be exemplified styrene, vinyltoluene,vinylxylene, α-methylstyrene, vinylnaphthalene and α-halogenatedstyrenes.

Further, as the monomer having a functional group for introducing ananion-exchange group, there can be exemplified styrene,bromobutylstyrene, vinyltolene, chloromethylstyrene, vinylpyridine,vinylimidazole, α-methylstyrene and vinylnaphthalene.

The above-mentioned aromatic monomers can be used in a single kind or ina combination of two or more kinds. It is, further, desired that thearomatic monomer is contained in the whole monomer components in anamount of at least not less than 25% by mass since it makes it possibleto greatly lower the resistance of the ion-exchange membrane that isobtained. It is, further, desired that the aromatic monomer is containedin an amount of less than 60% by mass in the whole monomer componentsfrom the standpoint of lowering the water content in the ion exchangerand, specifically, suppressing the peeling from the polyolefin typefilament base material when subjected to the swelling contractionrepetitively. The aromatic monomer is specifically desirably containedin the whole monomer components in an amount of 30 to 55% by mass.

When the ion-exchange resin is to be produced, in general, there is usedthe aromatic monomer having an ion-exchange group, e.g., the aromaticmonomer having an acid group such as sulfonic acid group or carboxylicacid group, or having a quaternary ammonium salt group. There can bealso used a method that directly produces the ion-exchange resin bypolymerization. However, the present invention does not employ the abovemethod. It is necessary that the invention employs a method that uses amonomer having a functional group that is capable of introducing anion-exchange group, and once forms an ion-exchange resin precursor and,thereafter, introduces the ion-exchange group into the precursor. Aswill be described later, the present invention must use the polyethyleneparticles. This is because if there is used a monomer having theion-exchange group, then a homogeneously polymerizable composition isnot obtained since the monomer is not compatible with the polyethyleneparticles.

(1-2) Crosslinkable Monomer;

The crosslinkable monomer is a monomer that is preferably used fordensifying the ion-exchange resin, for suppressing the swelling and forimproving the strength of the membrane. The above-mentioned aromaticmonomer is a monofunctional compound having a radically polymerizablegroup whereas the crosslinkable monomer is a polyfunctional compoundhaving not less than two radically polymerizable groups. Examples of thecrosslinkable monomer include, though not specifically limited, divinylcompounds such as divinylbenzene, divinylsulfone, butadiene,chloroprene, divinylbiphenyl, divinylnaphthalene, diallylamine anddivinylpyridine; and trivinyl compounds such as trivinylbenzene and thelike, which can be used alone or in a combination of two or more kinds.

The crosslinkable monomer is, usually, used in an amount of 1 to 20% bymass and, specifically, 2 to 10% by mass in the whole monomercomponents.

(1-3) Nitrogen-Containing Aliphatic Monomer;

The invention uses the nitrogen-containing aliphatic monomer togetherwith the above-mentioned aromatic monomer. The nitrogen-containingaliphatic monomer has a radically polymerizable group and anitrogen-containing group. By using the nitrogen-containing aliphaticmonomer in order to introduce the constituent unit derived from themonomer into the basic skeleton of the ion-exchange resin, it is madepossible to greatly improve the adhesiveness of the ion-exchange resinto the polyolefin type filament base material being aided by the use ofthe polyethylene particles that will be described later. Besides, theadhesiveness to the polyethylene particles is improved, too. As aresult, it is made possible to obtain an ion-exchange membrane thathighly adheres to the ion exchanger (mixture of the ion-exchange resinand the polyethylene) permeating into the voids in the base material andthat suppresses the water permeability down to lie in a predeterminedlow range.

The effect of improving the adhesiveness by the use of thenitrogen-containing aliphatic monomer was recognized as a phenomenon.Though the reason has not been clarified yet, the inventors estimate itas described below.

That is, if the constituent units are introduced by the use of thenitrogen-containing aliphatic monomer, then the main chain structuresappear to resemble each other between the ion-exchange resin and thepolyolefin that constitutes the base material depending, further, uponthe polarity of the nitrogen-containing groups. Therefore, closelyadhering property further increases in the interface between thepolyolefin type filament base material and the polyethylene phasederived from the polyethylene particles. Moreover, presence of theconstituent units derived from the aliphatic monomer imparts a suitabledegree of flexibility to the ion-exchange resin. As a result, theion-exchange resin follows up the filament base material and thepolyethylene phase even when it is subjected to the swelling-contractionrepetitively permitting less gaps to form between them.

As will be understood from the foregoing description, thenitrogen-containing aliphatic monomer must be a monofunctional radicallypolymerizable compound that has no aromatic group but has anethylenically unsaturated bond. The nitrogen-containing aliphaticmonomer having an aromatic group is not capable of impartingflexibility. The polyfunctional monomer such as a crosslinkable monomercauses the obtained ion-exchange resin to become dense and lowlyflexible. In neither case, therefore, the adhesiveness cannot beimproved.

From the above-mentioned point of view, the nitrogen-containingaliphatic monomer used in the present invention can be the compounds inwhich a polar nitrogen-containing group such as nitrile group or amidegroup is bonded to an aliphatic group that has a radically polymerizableunsaturated bond. Namely, the nitrogen-containing aliphatic monomer usedin the present invention can be nitrile group-containing monomers suchas acrylonitrile and methacrylonitrile; amide group-containing monomerssuch as acrylamide, methacrylamide, dialkylacrylamide,hydroxyethylacrylamide, isopropylacrylamide anddimethylaminopropylacrylamide; heterocyclic nitrogen-containinggroup-containing monomers such as acryloylmorpholine andvinylpyrrolidone; and amino group-containing monomers such as allylamineand the like, which may be used alone or in a combination of two or morekinds. Among them, the nitrile group-containing monomer is desired, andthe acrylonitrile is most desired from such standpoints that the effectfor improving the adhesiveness is exhibited to a maximum degree and thatthe capability of being copolymerized with the aromatic monomer is high.

The present invention uses the nitrogen-containing aliphatic monomer inan amount of 10 to 35% by mass and, specifically, 10 to 25% by mass inthe whole monomer components. This is because if the amount of thenitrogen-containing aliphatic monomer is too small, the adhesiveness isnot improved as desired. If the amount thereof is too large, on theother hand, properties such as the resistance and mechanical strength ofthe obtained ion-exchange membrane are impaired.

(1-4) Other Monomers;

The present invention uses the above-mentioned monomers as well as, asrequired, a comonomer that is capable of being copolymerized therewithin order to adjust the properties such as the strength and the likeproperties of the obtained ion-exchange resin, the copolymer being usedin an amount in a suitable range in which it will not impair the ratioof amounts of the above-mentioned monomers. The comonomer shall notimpair the functions of the above-mentioned nitrogen-containingaliphatic monomer, as a matter of course. Examples of the comonomer arestyrene, methylstyrene, chloromethylstyrene, α-methylstyrene, acrolein,methyl vinyl ketone, vinylbiphenyl and the like.

2. Polymerization Initiators;

As the polymerization initiator, there can be used those that have beenknown per se. without any specific limitation. Concretely, there can beused such organic peroxides as octanoyl peroxide, lauroyl peroxide,tert-butylperoxy-2-ethyl hexanoate, benzoyl peroxide, tert-butylperoxyisobutylate, tert-butylperoxy laurate, tert-hexylperoxy benzoate anddi-tert-butyloxy cyclohexane.

The polymerization initiator is used in an amount of, preferably, 0.1 to20 parts by weight and, more preferably, 0.5 to 10 parts by weight per100 parts by weight of the whole monomer components.

3. Polyethylene Particles;

The polymerizable composition used in the invention is blended with thepolyethylene particles. That is, being blended with the finepolyethylene particles, the polymerizable composition is imparted with asuitable degree of viscosity and spinnability and, therefore, adheresevenly to the polyolefin type filament base material. When thepolymerizable composition is polymerized, the fine polyethyleneparticles form a continuous phase that is distributed like a sea. Theion-exchange resin is distributed like islands in the sea-likecontinuous phase to thereby form a sea-islands structure. Here, noion-exchange group is introduced into the polyethylene phase even in thestep of introducing the ion-exchange groups that will be describedlater. Therefore, the water content is suppressed to be low in the ionexchanger (mixture of the ion-exchange resin and the polyethylene) thathas permeated into the voids in the polyolefin type filament basematerial. As a result, the ion exchanger is not easily peeled off thepolyolefin type filament base material despite of having undergone theswelling and drying (contraction).

The fine polyethylene particles are the same as those used by the methoddescribed in the patent document 2 (Japanese Patent Publication No.6-37568) and, usually, comprise, preferably, fine particles having aparticle size of not larger than 20 μm. That is, the polymerizablecomposition used in the present invention must assume the form of apaste and must have a suitable degree of viscosity and spinnability. Ifthe particle size of the fine polyethylene particles is too large,however, the polymerizable composition exhibits a decreased viscosityand becomes difficult to be evenly adhered to the polyolefin typefilament base material. Besides, the above-mentioned sea-islandsstructure that is formed upon polymerizing the polymerizable compositionassumes a size that is too large resulting in a decrease in the adhesionbetween the ion-exchange resin and the polyethylene.

Moreover, the particles of a spherical shape are preferred to theamorphous particles obtained by the mechanical pulverization from such astandpoint that the particles are homogeneously distributed in thepolymerizable composition to secure a viscosity that contributes toattaining favorable applicability.

Though there is no particular limitation, the polyethylene for formingthe fine particles is the one that has a melting point lower than thatof the polyolefin for forming the filament base material that will bedescribed later and, most desirably, is a low-density polyethylenehaving a melting point of, for example, not higher than 120° C. (e.g.,having a density of not less than 0.910 g/cm³ but less than 0.930g/cm³). In the step of polymerizing the polymerizable composition thatwill be described later, the fine polyethylene particles are at leastpartly melted by heat and form a sea-like continuous phase that is incontact with the filament base material. At this moment, upon using thefine particles of polyethylene, it is made possible to form a continuousphase of polyethylene that is distributed like a sea being closelyadhered to the filament base material and, therefore, it is allowed tofurther increase the adhesiveness of the ion exchanger to the filamentbase material.

The above polyethylene particles are used in an amount of 50 to 120parts by mass and, specifically, 55 to 100 parts by mass per 100 partsby mass of the monomer components. If the polyethylene particles areused in too large amounts, the ion-exchange capability of theion-exchange membrane is impaired. If the polyethylene particles areused in too small amounts, on the other hand, the adhesiveness isimpaired between the ion exchanger (polymer component containing theion-exchange resin and the polyethylene) in the membrane and thepolyolefin base material, and the ion-exchange membrane having desiredproperties is not obtained.

4. Other Blending Agents;

The polymerizable composition for forming the ion-exchange resinprecursor used in the invention may be blended with a plasticizer suchas dioctyl phthalate (DOP) or acetyltributyl citrate for adjusting theapplicability thereof, an epoxy compound such as ethylene glycoldiglycidyl ether for trapping the hydrochloric acid generated by thethermal decomposition of the monomer component, and various other knownadditives in amounts in a range in which they do not impair theion-exchange properties of the membrane that is finally formed or do notimpair the functions of the above-mentioned nitrogen-containingaliphatic monomer and the polyethylene particles.

As required, further, it is also allowable to add the known thickenersin addition to the polyethylene particles to adjust the viscosity of thepolymerizable composition so that it is more evenly adhered to thepolyolefin type filament base material. As the thickener, there can beexemplified polyvinyl chloride, nitrile-butadiene rubber,styrene-butadiene rubber and hydrogenated products thereof, which areadded in an amount, desirably, in a range of 0 to 30 parts by mass per100 parts by mass of the whole monomer components in the polymerizablecomposition. Due to the addition of the thickeners, the polymerizablecomposition can be imparted with a suitable degree of viscosity withoutthe need of increasing the amount of the fine polyethylene particles toomuch. Use of the polyvinyl chloride is most desired since it is capableof imparting viscosity to a sufficient degree despite of being added insmall amounts.

The polymerizable composition for forming the ion-exchange resinprecursor containing the above-mentioned various components can beeasily prepared by homogeneously mixing various components together.

<Production of the Ion-Exchange Membranes>

The ion-exchange membrane of the present invention is produced byapplying the above-mentioned polymerizable composition for forming theion-exchange resin precursor onto the polyolefin type filament basematerial, polymerizing the polymerizable composition in a state of beingfilled in the voids in the filament base material and, thereafter,introducing the ion-exchange groups into the ion-exchange resinprecursor that is formed by polymerization.

The base material of polyolefin type filaments works as a member forreinforcing the ion-exchange membrane, i.e., maintains the shape of themembrane and imparts a practical degree of strength to the membrane.

The filament base material referred to in the invention, generally,stands for a fabric formed by the aggregation of fibrous constituentunits. There is no specific limitation on the form of the filament basematerial, which, therefore, may be a woven fabric, a nonwoven fabric ora mesh. In general, however, the woven fabrics such as plain fabric,twill and woven mesh are desired from the standpoint of retaining theshape of the ion-exchange membrane and strength. In these woven fabrics,further, the intersecting points of single yarns may have beenheat-melt-adhered.

Furthermore, the filament base material may be the one formed by usingmonofilaments or may be the one formed by using multifilaments that areobtained by intertwisting a plurality of monofilaments (single yarns).However it is prefer that uses the one that is formed by usingmonofilaments. Namely, the multifilament is the one obtained byintertwisting a plurality of monofilaments, and provides an increasedarea of contact with the polymerizable composition yielding, therefore,an increased anchoring effect which is advantageous in obtaining anincreased strength of adhesion accompanied, however, by such a defectthat it is expensive. Therefore, the present invention uses theabove-mentioned nitrogen-containing aliphatic monomer to obtain anincreased strength of adhesion even when there are used inexpensivemonofilaments. Namely, the present invention favorably uses the basematerial made from monofilamens, which is a great advantage of theinvention.

The base material made from such filaments helps maintain a sufficientdegree of strength of the ion-exchange membrane that is obtained. Fromthe standpoint of maintaining the membrane resistance to remain low, onthe other hand, it is desired that the filament base material assumes 10to 300 mesh. It is, further, desired that the warps and wefts formingthe woven fabric have a filament diameter in a range of 10 to 250 denier(20 to 200 μm) in order to maintain the strength of the ion-exchangemembrane and to suppress an increase in the resistance caused by anincrease in the thickness of the membrane. Similarly, in order to attaina balance between the strength of the ion-exchange membrane and theresistance of the membrane, the membrane using the base filamentmaterial has a thickness of 50 to 500 μm and an opening area of 20 to60%.

Moreover, the polyolefin for forming the filament of the base materialis not specifically limited, and there can be used polyethylene;polypropylene; poly 1-butene; poly 4-methyl-1-pentene; or a random or ablock copolymer of α-olefins such as ethylene, propylene, 1-butene, or4-methyl-1-pentene. Specifically, the polyethylene is most desired fromthe standpoint of exhibiting a high degree of affinity to the monomercomponent in the polymerizable composition and maintaining a high degreeof adhesiveness between the base material and the ion exchanger.

Further, the filament base material that is used should, desirably, havea melting point higher than the melting point of the polyethyleneparticles so will not to undergo the thermal deformation when it ispolymerized as will be described below but so as to form a sea-likecontinuous phase of the polyethylene derived from the above polyethyleneparticles. It is, therefore, desired that the filament base material hasa melting point of, for example, not lower than 120° C.

From the above-mentioned point of view, therefore, a high-densitypolyethylene having a density of not less than 0.930 g/cm³ is,preferably, used as the polyolefin for forming the filament basematerial.

Moreover, the polyethylene may have a very high molecular weight asproposed by the patent document 1. However, the polyethylene of such avery high molecular weight is not advantageous in cost. Accordingly, thepolyethylene may be the one that has a molecular weight lying in anordinary range (e.g., having a weight average molecular weight of lessthan 1×10⁵).

The polymerizable composition is filled in the voids in the filamentbase material by, for example, dipping the filament base material in avessel filled with the polymerizable composition. The polymerizablecomposition, however, can also be filled by spraying instead of dipping.

After the voids have been filled with the polymerizable composition asdescribed above, the polyolefin type filament base material is fed intoa polymerization apparatus such as a heating oven and is heated so thatthe polymerizable composition is polymerized.

The step of polymerization, usually, employs a method in which thepolyolefin type filament base material containing voids filled with thepolymerizable composition is sandwiched by films of a polyester or thelike, and is heated starting from ordinary temperature under theapplication of a pressure. The pressure is, usually, about 0.1 to about1.0 MPa, and is produced by using an inert gas such as nitrogen or byusing rolls. Due to the application of pressure, the polymerization iscarried out in a state where an excess of the polymerizable compositionpresent in the interface of the filament base material on the outer sidethereof is pushed into the voids in the filament base material,effectively preventing the occurrence of resin reservoirs.

Further, the polymerization conditions are dependent upon the kind ofthe polymerization initiator and the kind of the monomer. In the presentinvention, however, the polymerization is carried out at a temperaturelower than the melting point of the polyolefin type filament basematerial but higher than the melting point of the polyethyleneparticles, e.g., in a temperature range of about 80 to about 120° C.This makes it possible to melt-flow the polyethylene particlessimultaneously with the formation of a polymer (ion-exchange resinprecursor) while preventing the polyolefin type filament base materialfrom being deformed and, therefore, to form a continuous phase ofpolyethylene that is distributed like a sea.

The polymerization time differs depending on the polymerizationtemperature and the like but is, usually, about 3 to about 20 hours.

The ion-exchange resin precursor formed by the above polymerizationoperation is distributed like islands being surrounded by the continuousphase of polyethylene that is distributed like a sea in the voids in thefilament base material, but remains partly in contact with the surfaceof the filament base material.

Here, the polymer or the ion-exchange resin precursor obtained asdescribed above has a functional group for introducing an ion-exchangegroup but has no ion-exchange group. Therefore the ion-exchange groupsare introduced after the above-mentioned step of polymerization.

The ion-exchange groups are introduced by a method known per se. When,for example, a cation-exchange membrane is to be produced, theion-exchange groups are introduced by such a treatment as sulfonation,chlorosulfonation, phosphoniation or hydrolysis. When an anion-exchangemembrane is to be produced, the ion-exchange groups are introduced bysuch a treatment as amination or alkylation.

<Ion-Exchange Membranes>

The ion-exchange membrane thus obtained has a structure in which thevoids in the filament base material are filled firmly with the ionexchanger that comprises the ion-exchange resin distributed like islandsand the continuous phase of polyethylene distributed like a sea.

In the ion-exchange membrane, the sea-like continuous phase ofpolyethylene is firmly adhered to the surface of the filament basematerial. Further, constituent units derived from thenitrogen-containing aliphatic monomer have been introduced into theion-exchange resin that is in contact with the surface of the filamentbase material. Therefore, a high degree of adhesiveness is obtainedamong the ion-exchange resin, the sea-like continuous phase ofpolyethylene and the filament base material. Accordingly, the ionexchanger is firmly fixed to the filament base material.

Therefore, the ion-exchange membrane of the present invention has awater permeability which is as low as 50 ml/(m²·hour) or less and,specifically, 25 ml/(m²·hour) or less as measured by using water under apressure of 0.1 MPa. The water permeability is measured by a methoddescribed in Examples appearing later. The smaller the value of waterpermeability, the higher the adhesiveness between the ion exchanger andthe filament base material forming less gaps in the membrane despite itis swollen-dried (contracted) repetitively. Specifically, even when thebase material is made of easily available monofilaments of apolyethylene having an ordinary molecular weight, low water permeabilityis maintained as described above offering a very great industrialadvantage from the standpoint of production cost.

Upon introducing the ion-exchange groups, the ion-exchange membrane ofthe present invention has a suitable ion-exchange capacity which is, forexample, about 0.1 to about 2.5 meq/g—dry mass. Here, since a highdegree of adhesiveness (low water permeability) has been realizedbetween the ion exchanger and the filament base material, theion-exchange membrane features excellent durability and a currentefficiency of, usually, 60 to 85% and, specifically, as high as 65 to80%. Moreover, the ion-exchange membrane, usually, has a thickness of 60to 550 μm and a Mullen burst strength of 0.2 to 2.0 MPa. Despite ofhaving such a large strength, the ion-exchange membrane exhibits amembrane resistance of as low as about 5 to about 25 Ω·cm² in a 0.5M—NaCl aqueous solution. Being made from the polyolefin, the basematerial exhibits excellent resistance against the heat, mechanicalstrength and resistance against chemicals, as a matter of course.

The ion-exchange membrane of the present invention is cut into asuitable size, and is put to use or is placed in the market.

EXAMPLES

The invention will now be described by the following ExperimentalExamples.

Properties of the filament base materials and of the ion-exchangemembranes were measured by the following methods.

1. Melting Points of the Filament Base Materials and of the PolyethyleneParticles

Measured by using the DSC-220C manufactured by Seiko Instruments Inc.The base material was punched into a circular shape 5 mm in diameter.Several circular materials were overlapped one upon the other to be 3 mgwhile the polyethylene particles were weighed to be 3 mg and were usedas a sample for measurement. They were laid on an open sample pan madeof aluminum having a diameter of 5 mm, and on which a clamping cover wasplaced and was fitted in the aluminum pan using a sample sealer. In anitrogen atmosphere, the temperature was elevated from 30° C. up to 180°C. at a rate of 10° C./min. to take a measurement. The temperature at amaximum point on a melting endothermic curve was regarded to be themelting point of the base material. When there were a plurality of peakson the melting curve, the temperature of a peak having the largest peakarea was regarded to be the melting point of the base material.

2. Opening Area of the Filament Base Material

Calculated from the diameter (μm) of the filament constituting the basematerial and the mesh count in compliance with the following formula,

Opening area (%)=(opening)²/(opening+filament diameter)²  (1)

wherein,

-   -   opening (μm)=25400/mesh count−filament diameter (μm),    -   mesh count=number of filaments per inch.

3. Water Permeability of the Ion-Exchange Membrane

The ion-exchange membrane was held in a cylindrical cell, 50 ml of waterwas poured from the upper part thereof, and a pressure of 0.1 MPa wasapplied from the upper side. In this state, the amount of water W_(p)wpermeating through the ion-exchange membrane in an hour was measured,and the water permeability was calculated in compliance with thefollowing formula. In this case, the effective area of the membrane was12.6 cm².

Water permeability (ml/(m²×hour))=W _(pw)/(S×t)  (2)

wherein,

-   -   S: effective area (m²) of the membrane,    -   t: testing time (hour).

4. Ion-Exchange Capacity and Water Content of the Ion-Exchange Membrane

The ion-exchange membrane was dipped in a 1 mol/L—HCl aqueous solutionfor not less than 10 hours.

Thereafter, in the case of the cation-exchange membrane, the counterions of the ion-exchange groups were substituted for the sodium ionsfrom the hydrogen ions in a 1 mol/L—NaCl aqueous solution, and theamount of the free hydrogen ions (A mol) was determined by apotentiometric titrator (COMTITE-900 manufactured by Hiranuma SangyoCo., Ltd.) by using a sodium hydroxide aqueous solution.

On the other hand, in the case of the anion-exchange membrane, thecounter ions were substituted for the nitric acid ions from the chlorideions in a 1 mol/L—NaNO₃ aqueous solution, and the amount of the freechloride ions (A mol) was determined by the potentiometric titrator(COMTITE-900 manufactured by Hiranuma Sangyo Co., Ltd.) by using asilver nitrate aqueous solution.

Next, the same ion-exchange membrane was dipped in the 1 mol/L—NaClaqueous solution for not less than 4 hours, and was washed with theion-exchanged water to a sufficient degree. Thereafter, the water on thesurface was wiped off with a tissue paper, and the mass (Wg) of themembrane was measured while it was wet. Moreover, the ion-exchangemembrane was dried at 60° for 5 hours under reduced pressure, and wasmeasured for its weight (Dg) while it was dry. Based on the abovemeasured values, the ion-exchange capacity and water content of theion-exchange membrane were found in compliance with the followingformulas,

Ion-exchange capacity [meq/g—dry mass]=A×1000/D

Water content [%]=100×(W−D)/D

5. Thickness of the Ion-Exchange Membrane

The ion-exchange membrane was dipped in a 0.5 mol/L—NaCl aqueoussolution for not less than 4 hours. Thereafter, the water on the surfaceof the membrane was wiped off with a tissue paper, and the thickness ofthe membrane was measured by using a micrometer MED-25PJ (manufacturedby Mitsutoyo Co.).

6. Resistance of the Ion-Exchange Membrane

The ion-exchange membrane was held in a 2-compartment cell havingplatinum black electrodes. The cell was filled with a 0.5 mol/L—NaClaqueous solution on both sides of the ion-exchange membrane, and theresistance across the electrodes was measured at 25° C. by using an ACbridge circuit (at a frequency of 1,000 cycles per sec.). A membraneresistance (Ω·cm²) was found from a difference between the resistanceacross the electrodes in this case and the resistance across theelectrodes measured without installing the ion-exchange membrane. Theion-exchange membrane used for the above measurement was the one thathad been equilibrated, in advance, in a 0.5 mol/L—NaCl aqueous solution.

7. Viscosity of the Polymerizable Composition

The polymerizable composition was measured for its viscosity at 25° C.by using a single cylindrical rotary viscometer, VISCOTESTER VT-06,(manufactured by RION Co., Ltd.).

8. Current Efficiency of the Ion-Exchange Membrane

In the case of the cation-exchange membrane, there was used a2-compartment cell having the following constitution.

Anode (Pt plate) (0.5 mol/L—NaOH aqueous solution)/cation-exchangemembrane/(3.0 mol/L—NaOH aqueous solution) cathode (Pt plate)

After an electric current was flown at a current density of 10 A/dm² forone hour at a liquid temperature of 25° C., the solution on the side ofthe anode was recovered. Concentrations of the sodium hydroxide in therecovered solution and in the initial solution were determined by apotentiometric titrator (Auto Titrator manufactured by KEM Co.) using asulfuric acid aqueous solution, and current efficiencies were calculatedin compliance with the following formula.

In the case of the anion-exchange membrane, there was used a2-compartment cell having the following constitution.

Anode (Pt plate) (1.0 mol/L—sulfuric acid aqueoussolution)/antion-exchange membrane/(0.25 mol/L—sulfuric acid aqueoussolution) cathode (Pt plate)

After an electric current was flown at a current density of 10 A/dm² forone hour at a liquid temperature of 25° C., the solution on the side ofthe cathode was recovered. Concentrations of the sulfuric acid in therecovered solution and in the initial solution were determined by thepotentiometric titrator (Auto Titrator manufactured by KEM Co.) using asodium hydroxide aqueous solution, and current efficiencies werecalculated in compliance with the following formula.

Current efficiency (%)=(C _(B) −C _(S))/(I×t/F)×100

wherein,

-   -   C_(B): concentration of the initial solution,    -   C_(S): concentration of the solution recovered after the current        has been flown,    -   I: current value (A),    -   t: current-flowing time (sec),    -   F: Faraday's constant (96500 C/mol).        9. Testing after Having Repeated the Treatment with the Hot        Water of 80° C.

A treatment consisted of dipping the ion-exchange membrane in pure waterof 80° C. for one hour and then dipping the ion-exchange membrane inpure water of 25° C. for not less than one hour. The treatment wasrepeated 10 times and, thereafter, the ion-exchange membrane wasmeasured for its water permeability and current efficiency.

Example 1

A mixture of the following recipe was prepared.

Styrene (St) 39.7 parts by mass Divinylbenzene (DVB)  5.2 parts by massChloromethylstyrene (CMS) 40.6 parts by mass Acrylonitrile (AN) 14.5parts by mass Acetyltributyl citrate (ATBC) 13.0 parts by massTert-butylperoxy-2-ethyl hexanoate (PBO)  7.3 parts by mass (Perbutyl Oproduced by NOF Co.)

To the above mixture was added 87.0 parts by mass of unmodulatedspherical low-density polyethylene particles PE1 (Flow Beads LE-1080produced by Sumitomo Seika Chemicals Co., Ltd. particle size; 6 μm,melting point; 105° C.), and the mixture thereof was stirred for 5 hoursto obtain a homogeneous polymerizable composition which possessed aviscosity of 2.2 (dPa·sec).

Next, there was provided the following high-density polyethylenemonofilament woven fabric (PE120).

High-density polyethylene monofilament woven fabric (PE120); Nippowerful network produced by NBC Meshtec Inc.)

Warp: 96 mesh—filament diameter of 106 μm (62 denier)

Weft: 76 mesh—filament diameter of 122 μm (71 denier)

Thickness: 260 μm

Opening area: 38%

Melting point: 130° C.

The polymerizable composition obtained above was applied onto the abovehigh-density polyethylene monofilament woven fabric (PE120). The wovenfabric was then covered on its both surfaces with a polyester film thatwas removable, and was polymerized at 95° C. for 5 hours.

The obtained membrane-like high molecular body was sulfonated with thechlorosulfonic acid at 40° C. for 2 hours to obtain a cation-exchangemembrane. Properties of the obtained cation-exchange membrane were asfollows:

Membrane thickness: 285 μm

Ion-exchange capacity: 1.4 meq/g—dry mass

Water content: 30%

Membrane resistance: 12.2 Ω·cm²

Water permeability: 0 ml/(m²·hour)

Current efficiency: 72%

Next, the cation-exchange membrane was subjected to the recurring testconducted at 80° C., and was measured for its water permeability andcurrent efficiency to be 0 ml/(m²·hour) and 68%, respectively. Theseproperties had not been almost deteriorated.

Examples 2 to 6

By using the components shown in Table 1, there were preparedpolymerizable compositions in the same manner as in Example 1. Table 1also shows viscosities of the obtained polymerizable compositions.

In Table 1, 40E and PHC are abbreviations of the following compounds.

-   -   40E: ethylene glycol diglycidyl ether (Epolight 40E, produced by        Kyoeisha Chemical Co., Ltd.)    -   PHC: 1,1-di-tert-butylperoxycyclohexane (Perhexa C, produced by        NOF Co.)

The cation-exchange membranes of the invention were then obtained in thesame manner as in Example 1 but changing the polymerization temperatureto 100° C. Table 2 shows the properties of the obtained cation-exchangemembranes and the results of the recurring test conducted at 80° C.

Example 7

There were provided the following unmodified spherical low-densitypolyethylene particles (PE2).

Unmodified spherical low-density polyethylene particles (PE2);

-   -   Flow Beads LE-2080 produced by Sumitomo Seika Chemicals Co.,        Ltd. Particle size: 11 μm    -   Melting point: 105° C.

By using the above unmodified spherical low-density polyethyleneparticles (PE2), a polymerizable composition of components shown inTable 1 was prepared.

The obtained polymerizable composition possessed a viscosity of 4.2(dPa·sec).

Next, as a polyolefin type monofilament base material, there wasprovided the following polypropylene woven fabric (PP).

Polypropylene woven fabric (PP);

Mesh count: 100

Filament diameter: 68 μm (30 denier)

Thickness: 128 μm

Opening area: 53%

Melting point: 168° C.

A cation-exchange membrane of the invention was obtained in the samemanner as in Example 1 but using the above polypropylene woven fabric(PP). Table 2 shows the properties of the obtained cation-exchangemembrane and the results of the recurring test conducted at 80° C.

Example 8

There were provided the following spherical ethylene-acrylic acidcopolymer particles (PE3).

Spherical ethylene-acrylic acid copolymer particles (PE3);

Flow Beads LE-209

Particle size: 10 μm

Melting point: 101° C.

Content of acrylic acid unit: 10%

By using the above spherical ethylene-acrylic acid copolymer particles(PE3), a polymerizable composition of components shown in Table 1 wasprepared. The polymerizable composition possessed a viscosity of 20.0(dPa·sec).

Next, a cation-exchange membrane of the invention was obtained in thesame manner as in Example 1. Table 2 shows the properties of theobtained cation-exchange membrane and the results of the recurring testconducted at 80° C.

Example 9

A polyvinyl chloride (PVC) was added as the thickener, and apolymerizable composition shown in Table 1 was prepared. Thepolymerizable composition possessed a viscosity of 1.5 (dPa·sec).

Next, a cation-exchange membrane of the invention was obtained in thesame manner as in Example 2. Table 2 shows the properties of theobtained cation-exchange membrane and the results of the recurring testconducted at 80° C.

Example 10

A mixture of the following recipe was prepared.

Chloromethylstyrene (CMS) 54.0 parts by mass Divinylbenzene (DVB)  4.0parts by mass Styrene (St) 30.0 parts by mass Acrylonitrile (AN) 12.0parts by mass Ethylene glycol diglycidyl ether (40E) (Epolight 40E,  2.0parts by mass produced by Kyoeisha Chemical Co., Ltd.)  1,1-di-tert-butylperoxycyclohexane (PBO) (Perhexa C,  7.3 parts by massproduced by NOF Co.)

To the above mixture was added 87.0 parts by mass of unmodulatedspherical low-density polyethylene particles (PE1), and the mixturethereof was stirred for 5 hours to obtain a homogeneous polymerizablecomposition which possessed a viscosity of 2.0 (dPa·sec).

Next, there was provided the following high-density polyethylenemonofilament woven fabric (PE200).

High-density polyethylene monofilament woven fabric (PE200); Nippowerful network produced by NBC Meshtec Inc.)

Warp: 156 mesh—filament diameter of 86 μm (50 denier)

Weft: 100 mesh—filament diameter of 86 μm (50 denier)

Thickness: 185 μm

Opening area: 32%

Melting point: 130° C.

The composition obtained above was applied onto the above high-densitypolyethylene monofilament woven fabric (PE200). The woven fabric wasthen covered on its both surfaces with a polyester film that wasremovable, and was polymerized at 100° C. for 5 hours. The obtainedmembrane-like high molecular body was dipped in a mixture of 15 parts bymass of an aqueous solution containing 30% of trimethylamine, 52.5 partsby mass of water and 22.5 parts by mass of acetone maintaining atemperature of 30° C. for 16 hours, and there was obtained a quaternaryammonium type anion-exchange membrane.

Table 2 shows the properties of the obtained anion-exchange membrane andthe results of the recurring test conducted at 80° C.

Example 11

The polymerizable composition of Example 1 was applied onto thehigh-density polyethylene monofilament woven fabric (PE200). The wovenfabric was then covered on its both surfaces with a polyester film thatwas removable, and was polymerized at 95° C. for 5 hours. The obtainedmembrane-like high molecular body was sulfonated with the chlorosulfonicacid at 40° C. for 2 hours to obtain a cation-exchange membrane.

Table 2 shows the properties of the obtained cation-exchange membraneand the results of the recurring test conducted at 80° C.

Example 12

By using the polymerizable composition of Example 1, a cation-exchangemembrane of the present invention was obtained in the same manner as inExample 7.

Table 2 shows the properties of the obtained cation-exchange membraneand the results of the recurring test conducted at 80° C.

Comparative Example 1

A polymerizable composition shown in Table 1 was prepared without,however, adding the nitrogen-containing aliphatic monomer, and acation-exchange membrane was obtained in the same manner as in Example1.

Table 2 shows the properties of the obtained cation-exchange membraneand the results of the recurring test conducted at 80° C. As compared toExample 1, the water permeability and the current efficiency had beendeteriorated. After the recurring test conducted at 80° C., theseproperties had been deteriorated further strikingly.

Comparative Examples 2 to 5

Polymerizable compositions of components shown in Table 1 were preparedby using the nitrogen-containing aliphatic monomer and the polyethyleneparticles in amounts very different from the amounts of Example 1. Theobtained polymerizable compositions possessed viscosities as shown inTable 1.

By using the obtained polymerizable compositions, cation-exchangemembranes were prepared in the same manner as in Example 2. InComparative Example 5, the viscosity of the polymerizable compositionwas so high that a homogeneous membrane-like product could not beobtained.

Table 2 shows the properties of the cation-exchange membranes obtainedin Comparative Examples 2 to 5 and the results of the recurring testconducted at 80° C.

Comparative Example 6

A polymerizable composition was prepared in the same manner as inExample 9 but without adding the nitrogen-containing aliphatic monomer,and a cation-exchange membrane was obtained in the same manner as inExample 9. Table 2 shows the properties of the obtained cation-exchangemembrane and the results of the recurring test conducted at 80° C.

Comparative Example 7

A polymerizable composition was prepared in the same manner as inExample 10 but without adding the nitrogen-containing aliphatic monomer,and an anion-exchange membrane was obtained in the same manner as inExample 10. Table 2 shows the properties of the obtained anion-exchangemembrane and the results of the recurring test conducted at 80° C.

TABLE 1 Components of polymerizable composition (parts by mass) Aromaticmonomer for introducing Crosslinking Nitrogen-containing exchange groupmonomer aliphatic monomer Other monomer Example Kind Amount Kind AmountKind Amount Kind Amount  1 St 39.7 DVB 5.2 AN 14.5 CMS 40.6  2 St 39.7DVB 5.2 AN 10.5 CMS 44.6  3 St 39.7 DVB 5.2 AN 29.0 CMS 26.1  4 St 39.7DVB 5.2 AN 14.5 CMS 40.6  5 St 39.7 DVB 5.2 AN 14.5 CMS 40.6  6 St 39.7DVB 5.2 DMAA 14.5 CMS 40.6  7 St 39.7 DVB 5.2 AN 14.5 CMS 40.6  8 St39.7 DVB 5.2 AN 14.5 CMS 40.6  9 St 39.7 DVB 5.2 AN 14.5 CMS 40.6 10 CMS54.0 DVB 4.0 AN 12.0 St 30.0 Comp. Ex. 1 St 39.7 DVB 5.2 — — CMS 55.1Comp. Ex. 2 St 39.7 DVB 5.2 AN 5.0 CMS 50.1 Comp. Ex. 3 St 39.7 DVB 5.2AN 38.0 CMS 17.1 Comp. Ex. 4 St 39.7 DVB 5.2 AN 14.5 CMS 40.6 Comp. Ex.5 St 39.7 DVB 5.2 AN 14.5 CMS 40.6 Comp. Ex. 6 St 39.7 DVB 5.2 — — CMS55.1 Comp. Ex. 7 CMS 54.0 DVB 4.0 — — St 42.0 Components ofpolymerizable composition (parts by mass) Viscosity of PolyethyleneOther blending Polymerization polymerizable powder agent initiatorcomposition Example Kind Amount Kind Amount Kind Amount (dPa · sec)  1PE1 87.0 ATBC 13.0 PBO 7.3 2.2  2 PE1 87.0 ATBC 13.0 PHC 7.3 1.9  3 PE187.0 ATBC 13.0 PHC 7.3 4.3  4 PE1 70.0 ATBC 11.0 PHC 7.3 1.5 40E 2.0  5PE1 104.0 ATBC 11.0 PHC 7.3 4.7 40E 2.0  6 PE1 87.0 ATBC 13.0 PHC 7.31.2  7 PE2 87.0 ATBC 13.0 PBO 7.3 4.2  8 PE3 87.0 ATBC 13.0 PBO 7.3 20.0 9 PE1 60.0 ATBC 13.0 PHC 7.3 1.5 PVC 30.0 10 PE1 87.0 40E 2.0 PHC 7.32.0 Comp. Ex. 1 PE1 87.0 ATBC 13.0 PBO 7.3 1.2 Comp. Ex. 2 PE1 87.0 ATBC13.0 PHC 7.3 1.4 Comp. Ex. 3 PE1 87.0 ATBC 13.0 PHC 7.3 5.3 Comp. Ex. 4PE1 40.0 ATBC 13.0 PHC 7.3 0.3 Comp. Ex. 5 PE1 130.0 ATBC 13.0 PHC 7.340.0 Comp. Ex. 6 PE3 87.0 ATBC 13.0 PHC 7.3 18.0 Comp. Ex. 7 PE1 87.040E 2.0 PHC 7.3 1.8

TABLE 2 Properties of ion-exchange membrane Ion-exchange Polyolefin typePolymerization Membrane capacity filament base temperature thicknessResistance [meg/g- Example material [° C.] [μm] [Q · cm²] dry mass] 1PE120 95 285 12.2 1.4 2 PE120 100 281 15.0 1.2 3 PE120 100 295 14.0 1.44 PE120 100 299 11.0 1.6 5 PE120 100 295 18.3 1.3 6 PE120 100 283 13.31.4 7 PP 95 163 6.8 1.4 8 PE120 95 317 8.7 1.8 9 PE120 100 279 12.8 1.410 PE200 100 208 12.0 1.4 11 PE200 95 214 12.0 1.5 12 PP 95 157 7.6 1.4Comp. Ex. 1 PE120 95 276 17.0 1.1 Comp. Ex. 2 PE120 100 278 16.0 1.2Comp. Ex. 3 PE120 100 314 9.0 1.6 Comp. Ex. 4 PE120 100 305 7.7 1.8Comp. Ex. 5 PE120 100 membrane could not be formed Comp. Ex. 6 PE120 100306 11.7 1.4 Comp. Ex. 7 PE200 100 215 9.7 1.5 Properties after treatedwith Properties of ion-exchange membrane hot water of 80° C. for 10times Water Water Current Water Current content permeability efficiencypermeability efficiency Example [%] [ml/m² · Hr] [%] [ml/m² · Hr] [%] 130 0 72 0 68 2 24 8 67 32 61 3 34 0 70 8 65 4 34 0 71 0 67 5 29 0 71 067 6 28 0 71 8 66 7 29 16 64 32 59 8 33 0 71 8 66 9 27 0 74 0 71 10 29 046 0 42 11 32 0 70 0 67 12 28 16 63 48 58 Comp. Ex. 1 22 80 62 250 55Comp. Ex. 2 23 56 64 128 56 Comp. Ex. 3 34 64 63 208 55 Comp. Ex. 4 36350 50 >1000 41 Comp. Ex. 5 membrane could not be formed Comp. Ex. 6 2556 67 136 56 Comp. Ex. 7 32 56 43 148 37

1. A polymerizable composition for forming an ion-exchange resinprecursor, said polymerizable composition containing a monomer componentand polyethylene particles in an amount of 50 to 120 parts by mass per100 parts by mass of said monomer component, wherein said monomercomponent contains an aromatic monomer for introducing ion-exchangegroups and a nitrogen-containing aliphatic monomer, saidnitrogen-containing aliphatic monomer being present in an amount of 10to 35% by mass in said monomer component.
 2. The polymerizablecomposition according to claim 1, wherein said nitrogen-containingaliphatic monomer is an acrylonitrile.
 3. The polymerizable compositionaccording to claim 2, wherein said polyethylene particles are unmodifiedpolyethylene particles.
 4. A method of producing an ion-exchangemembrane by applying the polymerizable composition of claim 1 onto apolyolefin type filament base material and polymerizing saidpolymerizable composition to form an ion-exchange resin precursor and,thereafter, introducing ion-exchange groups into said precursor.
 5. Themethod of producing the ion-exchange membrane according to claim 4,wherein said polyolefin type filament base material is a polyolefin typemonofilament base material.
 6. The method of producing the ion-exchangemembrane according to claim 4, wherein said polyolefin type filamentbase material is a polyethylene type filament base material.
 7. Anion-exchange membrane in which an ion exchanger is filled in the voidsin the polyolefin type filament base material, wherein: saidion-exchange membrane has a water permeability of not more than 50ml/(m²·hour) as measured by using the water under a pressure of 0.1 MPa;said the ion exchanger contains an aromatic ion-exchange resin and apolyethylene as the resin components; and said aromatic ion-exchangeresin contains a constituent unit derived from the nitrogen-containingaliphatic monomer.